Physiological measurement devices to be worn on the body are known, e.g., in the form of wrist watches with a pulse-measuring function or blood pressure meters also worn on the wrist or recently also measurement devices worn in a similar way for determining blood oxygen saturation. To some extent, these measurement devices are already in practical use on a wide scale. Measured-value-influencing means are not necessary and are not provided with all such measurement devices. Wrist watches with a pulse-measuring function in particular may also achieve a relatively high precision, which is at any rate completely adequate for the leisure sports area even without such correction means.
In the case of other mobile devices that are worn on the body and have, e.g., optical sensors for determination of oxygen saturation, determination of movement artifacts, and a corresponding correction of the primary measurement result play an important role and constitute a special challenge. It is known that movement sensors (e.g., acceleration meters) may be used to solve this problem. If a significant movement of the device is detected during a certain measurement phase, then the measured values obtained in that phase are discarded.
However, it has been found that these devices still do not operate completely satisfactorily and the wearing habits of the user are also important for their functionality. In particular, errors may occur due to a relatively loose mechanical connection between the body and the measurement device and may lead to deviations in the movement sequences between the two. An attempt to solve these problems by providing fastening means, which are supposed to ensure a tight and constant connection between the body and the measurement device, e.g., through a tight elastic wristband, substantially impair user acceptance (patient compliance) and thus have a negative effect on the market chances of the corresponding devices.
It is also conceivable for movements of a certain body area to be detected directly by a movement sensor (e.g., an acceleration meter) implanted in the body area where the measurement devices are usually worn and to use these movement signals detected either directly or in combination with movement signals detected in a comparable manner on the measurement device to eliminate or discard movement artifacts from primary measurement signals. An implanted movement sensor would be constantly available and could be placed in the body in such a way that it is not detectable from outside the body.
However, many potential users are frightened off from implantation and especially explantation as surgical procedures as well as by the mere idea of having an implant, so that even with this approach, user acceptance, on average, is not satisfactory. Furthermore, the medical cost to implement this approach is relatively high.
However, although analysis of other parameters, e.g., electromyogram (EMG) measurements sensed by surface leads for conduction of muscle activity, can provide information about whether the measurement device is in contact with the proper body area (EMG visible) or not (EMG invisible), such an analysis does not provide information about the amplitude or direction of movement of the measurement device with respect to the body area.